The present invention relates to a correlation degree operation apparatus, a parallel correlation degree operation apparatus and a correlation degree operation method each of which is effective in detecting motion vector of picture data and which is arranged to operate a degree of correlation between two types of picture data.
As a method of compressing motion picture data, there is known a method of reducing time redundancy with the use of information (motion vector) representing that a certain part in the just previous picture has moved to which place in the current picture.
As a method of extracting such motion vector, there is known a so-called block matching method in which a current frame picture (reference picture frame) is compared with the previous frame picture (candidate frame) and in which a block similar (highly correlative) to a certain block (reference picture block) of the current frame picture, is extracted from the previous frame picture, and the motion vector is then detected. This block matching method is widely used for motion compensation prediction of picture compression coding.
According to such a block matching method, there is operated a degree of correlation between one reference picture block and each of a plurality of candidate blocks of the previous frame picture, there is selected the candidate block having the highest correlation degree, and the motion vector is then detected. To obtain the correlation between two picture blocks, it is required to operate the picture element data of each picture block. Further, to enhance the possibility of selecting a block high in correlation degree, recent picture compression technology tends to widen the search area to increase the number of candidate blocks. Thus, there is increasingly needed a correlation degree operation apparatus capable of operating, at high speed, a degree of correlation between two picture blocks.
As a correlation degree operation apparatus of prior art, there is known the type in which a plurality of operation devices each for operating a correlation degree are concurrently operated to achieve a high-speed process.
For example, the correlation degree operation apparatus disclosed by Japanese Patent Laid-Open Publication No. 6-451304 has the following arrangement. When the size of a reference picture block is equal to (M.times.N) picture elements and the number of candidate blocks is also equal to (M.times.N), there are disposed, in an M.times.N matrix, (M.times.N) operation units comprising picture element value storage registers, multiplexers and differential absolute value operation devices, the output data lines of the operation units are pipeline-connected to one another through adders, and the picture element data of a reference picture block and candidate blocks are supplied to the differential absolute value operation devices in a predetermined order. It is therefore possible to successively supply, per each clock cycle, the sum of differential absolute values representing an evaluation index of correlation degree. This achieves a high-speed operation of correlation degree.
However, the correlation degree operation apparatus of prior art has the following problems.
In this correlation degree operation apparatus, there can be operated degrees of correlation of only (M.times.N) candidate blocks with respect to a reference picture block having (M.times.N) picture elements. This makes it very difficult to increase the number of candidate blocks by extending the search area in order to enhance the possibility of selecting a candidate block high in correlation degree.
When compressing pictures according to the MPEG which is the international standards for picture compression, to assure a high picture quality with a reduced amount of codes, the search area is extended to provide, for example, 32.times.32 or 48.times.48 candidate blocks for a reference picture block having 16.times.16 picture elements. Accordingly, it is inevitable to provide a correlation degree operation apparatus which assures a high-speed process even though the search area is extended and which is small in circuit area.